/**
 *    Copyright ${license.git.copyrightYears} the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.mybatis.generator.internal.util;

import java.lang.reflect.Array;

/**
 * This class is from javapractices.com:
 * 
 * http://www.javapractices.com/Topic28.cjp
 * 
 * Collected methods which allow easy implementation of <code>hashCode</code>.
 * 
 * Example use case:
 * 
 * <pre>
 * public int hashCode() {
 *   int result = HashCodeUtil.SEED;
 *   // collect the contributions of various fields
 *   result = HashCodeUtil.hash(result, fPrimitive);
 *   result = HashCodeUtil.hash(result, fObject);
 *   result = HashCodeUtil.hash(result, fArray);
 *   return result;
 * }
 * </pre>
 */
public final class HashCodeUtil {

  /**
   * An initial value for a <code>hashCode</code>, to which is added contributions from fields. Using a non-zero value
   * decreases collisons of <code>hashCode</code> values.
   */
  public static final int SEED = 23;

  /**
   * booleans.
   *
   * @param aSeed
   *          the a seed
   * @param aBoolean
   *          the a boolean
   * @return the int
   */
  public static int hash(int aSeed, boolean aBoolean) {
    return firstTerm(aSeed) + (aBoolean ? 1 : 0);
  }

  /**
   * chars.
   *
   * @param aSeed
   *          the a seed
   * @param aChar
   *          the a char
   * @return the int
   */
  public static int hash(int aSeed, char aChar) {
    return firstTerm(aSeed) + aChar;
  }

  /**
   * ints.
   *
   * @param aSeed
   *          the a seed
   * @param aInt
   *          the a int
   * @return the int
   */
  public static int hash(int aSeed, int aInt) {
    /*
     * Implementation Note Note that byte and short are handled by this method, through implicit conversion.
     */
    return firstTerm(aSeed) + aInt;
  }

  /**
   * longs.
   *
   * @param aSeed
   *          the a seed
   * @param aLong
   *          the a long
   * @return the int
   */
  public static int hash(int aSeed, long aLong) {
    return firstTerm(aSeed) + (int) (aLong ^ (aLong >>> 32));
  }

  /**
   * floats.
   *
   * @param aSeed
   *          the a seed
   * @param aFloat
   *          the a float
   * @return the int
   */
  public static int hash(int aSeed, float aFloat) {
    return hash(aSeed, Float.floatToIntBits(aFloat));
  }

  /**
   * doubles.
   *
   * @param aSeed
   *          the a seed
   * @param aDouble
   *          the a double
   * @return the int
   */
  public static int hash(int aSeed, double aDouble) {
    return hash(aSeed, Double.doubleToLongBits(aDouble));
  }

  /**
   * <code>aObject</code> is a possibly-null object field, and possibly an array.
   * 
   * If <code>aObject</code> is an array, then each element may be a primitive or a possibly-null object.
   *
   * @param aSeed
   *          the a seed
   * @param aObject
   *          the a object
   * @return the int
   */
  public static int hash(int aSeed, Object aObject) {
    int result = aSeed;
    if (aObject == null) {
      result = hash(result, 0);
    } else if (!isArray(aObject)) {
      result = hash(result, aObject.hashCode());
    } else {
      int length = Array.getLength(aObject);
      for (int idx = 0; idx < length; ++idx) {
        Object item = Array.get(aObject, idx);
        // recursive call!
        result = hash(result, item);
      }
    }
    return result;
  }

  // / PRIVATE ///
  /** The odd prime number. */
  private static final int fODD_PRIME_NUMBER = 37;

  /**
   * First term.
   *
   * @param aSeed
   *          the a seed
   * @return the int
   */
  private static int firstTerm(int aSeed) {
    return fODD_PRIME_NUMBER * aSeed;
  }

  /**
   * Checks if is array.
   *
   * @param aObject
   *          the a object
   * @return true, if is array
   */
  private static boolean isArray(Object aObject) {
    return aObject.getClass().isArray();
  }
}
